Process of preparing magnesia and sulphur dioxide



Feb- 4, 1941- R GRlEssBAcH Erm. 2,230,592

PROCESS DF PREPARING MAGNSIA AND SULPHUR DIOXIDE l Filed sept. 15, 1939THE: A-r oRNEYs Patented Feb. 4, 1941 UNITED STATES PATENT OFFICEPROCESS F PBEPARING MAGNESIA AND SULPHUB DIOmE Robert Griessbach,Wollen, Kreis Bitterfeld,

Walther Siitterlln,

Bitterfeld, and Hans Application September 15, 1939, Serial No. 295,052In Germany February 2, 1937 2 Claims.

The present invention relates to a process of preparing magnesia andsulphur dioxide.

The known processes of reducing magnesium sulphate by means of coal donot yet show an industrially useful way for obtaining magnesium oxideand onlyone uniform sulphur compound in a practically complete yield.The main difliculties reside in the fact that, on using a deficiency ofcoal, the reduction does not occur quantitatively; on usingan excess ofcoal, however,` S, HzS, COS .and CS2 are formed besides SO2. It has,therefore, been suggested to effect the re'- duction with an excess ofcoal, but to let follow as second operative step a chlorinating oroxidizing roasting. These processes, obviously, have the drawback thatother sulphur compounds are formed besides sulphur dioxide, the workingup of which compounds is very dicult.

Now we have found a process by which it is possible in one singleoperation to reduce magnesium sulphate practically completely so as toform magnesium oxide, a gas being simultaneously obtained which containsthe sulphur only in the form of sulphur dioxide in such a concentrationthat sulphurtrioxide may be'prepared therefrom in a Contact apparatusattached 'to the reaction device.- This decomposition of the magnesiumsulphate is attained by subdividing the reduction furnaceinto threezones. upper, feebly oxidizing zone the mixture of magnesium sulphateand coal introduced which contains a deficiency of coal is pre-heated.During its migration it passes the middle zone where the temperaturerises from about 700 C. to 900 C. In this Zone the coal has a reducingaction. The. gaseous phase is kept neutral in that zone of the furnace.When 'the contentof the fui'- nace reaches the lower zone the coal isalready consumed. The unchanged magnesium sulphate still present is thencompletely reduced in a reducing gaseous medium. By the partialcombustion of the gas introduced at the lower end of the furnace for thepurpose of heating the interior of the furnace, carbon dioxide and/orsteam are formed, the formation of magnesium sulphide being preventedthereby. The temperatures in this zone are at about 1000 C.

By this mode of working the above mentioned drawbacks of the knownprocesses of decomposing magnesium sulphate are avoided. On the one handthe formation of sulphur and hydrogen sulphide is practically preventedby the use of a deficiency of coal in the middle zone and on the otherhand the unchanged magnesium sulphate is likewise reduced so as to formmagnesium In the oxide by the reducing action of the gases in the lowerzone. Any reduced sulphur gases which may be formed in this zone arecompletely oxidized in the upper zone by the air blown in so as to formsulphur dioxide. 5

By the slowly rising temperatures in the middlezone it becomes alsopossible that in the range of higher temperatures a sufficient quantityof magnesium oxide is present to prevent the hitherto .technicallyinevitable agglutination of the charge of the furnace. Generally acontent of 50 per cent. to 70 p er cent. of magnesium oxide issufficient for the mixture when it enters the third zone of about 900 C.to 1000- C.

For carrying out the reduction there may, for instance, be used arevolvingfurnace with a Y gas-tight Aclosure at one side and an inletfor gas and air at different parts of the furnace.

Of course, an inlet for gas and air according to the conditions of theinvention may likewise be mounted at other furnaces, for instance, ashaft kiln, a tunnel kiln or the-like. As heating and reducing gas theremay be used a gas containing hydrogen, carbon monoxide or a gasiedliquid reducing lagent. The reducing coal should be poor in ash.`

'll'lie following example serves to illustrate the invention, but it' isnot intended to limit it thereto; the parts areby weight:

The upper end of a revolving furnace is charged with a mixture of 100parts of kieserite and 8.5 parts of a granular coke from lignite. Theheating gas (generator gas) and the corresponding quantities of air areintroduced through'burners one of which is mounted at .the 35 lowest endof the lower third of the furnace and is fed in a strongly reducing way(3 to 5 per cent. of Hz--CO remain unburnt) in order to decompose theresidues of MgSO4 Whereas the other burner is situated at the limitbetween the lower 40 third andthe middle zone, the'addition of air tothe heatinggasbeing regulated there so that neither a reducing nor anoxidizing but solely a Y neutral burning atmosphere is formed by whichthe temperature is brought to about 900 C. At 45 the limit between themiddle and the upper zone4 where the gases in the furnace have cooled toabout 700 C. by the action of the material introduced a new oxidizingzone is created by the addition of air to such an extent that at theinlet end the waste gases are composed of about 1 per cent. of O2, 18 to20 per cent. of CO2 and 8 to 10 per cent. of SO2. Under these workingconditions the gases contain neither other sulv phur compounds norelementary sulphur. The

product obtained is practically completelyl reduced and contains about95 per cent. of MgO (residue: impurities from the kieserite and ashportions of Vthe coal.)

If the magnesia thus obtainedis to be furthe -treated so as to obtainsintered magnesite, its high temperature is with advantage directlyutilized by heating the reaction product, which by the necessary flux ofiron oxide (for instance, roasted pyrites) to the mixture of kieseriteand coal has been given the usual composition, to about 1400 C. in acorrespondingly lined prolonged part of the furnace in an oxidizingatmosphere. Y

It is also possible, instead of using coal and gas, to perform thereduction with the aid of gas `alone, whereby a magnesia is obtainedwhich is free from coal ash. In this case the material is heated, in theiirst oxidizing zone, to about 700 C., the temperature is then slowlyraised to about 1000 C., 900 C. being not exceeded until the materialcontains about 50 to 70 per cent. of magnesia.

The invention is of course not limited to the exact details described,for obvious modications may occur to a person skilled in the art.

What we claim is:

1. A process of preparing magnesia and sulphur dioxide by reduction ofmagnesium sulphate which comprises leading the material through anoxidizing preheating zone having a temperature of about 700 C. andreducing the material ina furnace heated in the interior at temperaturesrising up to about 900 C. Without sintering inv the presence-of a.reducing agent of the group consisting of coal and gas, said reducingagent being present in a quantity suilicient to effect full reduction ofno more than about 50 to '70 per temperatures rising up to about 900 C.Without sintering with coal in the presence ofv a neutral atmosphere,said coal being present in a quantity sumcient to effect full reductionof no more than about 50 to '70 per cent. of the magnesium sulphate tomagnesi'aand completing the reduction at temperatures rising up to about1000 C. while in contact with a gaseous reducing agent.

ROBERT GRIEssBAcH. WALTHER. s'I'rERLIN. HANS zIRNGIBL.

